Project III entails an examination of the Florida's Progress Monitoring and Reporting Network (PMRN)[unreadable] database containing multiple measures of multiple reading constructs on 300,000 children attending[unreadable] underachieving schools in the state of Florida. Approximately 124,000 new children enter the database each[unreadable] year in one of the six grade levels in which data are collected: kindergarten through Fifth grade. This[unreadable] extensive database is uniquely equipped to answer questions related to each of the six Center grant goals. It[unreadable] will be used to estimate the percentages of struggling readers who fit alternative classification criteria for[unreadable] learning disability in various domains (e.g., impaired decoding, impaired comprehension, etc.). It also will be[unreadable] used to examine how alternative classification criteria for learning disability (e.g., unexplained low[unreadable] achievement, inadequate growth) are related (i.e., do they classify the same children as learning disabled).[unreadable] We will examine the predictive validity of alternative classification criteria for learning disability, amd[unreadable] environmental variables in relation to alternative classifications (e.g., SES, performance level of the school,[unreadable] etc.) and their predictive validity. For the quantitative genetic studies, we will identify an usually large[unreadable] number (N = 9,000) of identical and fraternal twins within the PMRN sample in order to examine genetic and[unreadable] environmental influence on reading constructs, their relationships to each other, and to their growth over[unreadable] time. We will use the sample within the PMRN to examine differential heritability of reading ability vs.[unreadable] disability defined in alternative ways.